1. Technical Field
The present disclosure relates to delay circuits and more specifically to a programmable delay circuit suitable for delaying high speed signals.
2. Related Art
Delay circuits are often used to delay a sequence of digital values of interest. The magnitude (“delay magnitude”) by which a signal is delayed can be specified from external sources (e.g., by a user or other portion of the circuit), and a corresponding delay circuit is referred to as a programmable delay circuit. The potential delay magnitudes, including the minimum, maximum and intermediate values, defines the span of delays provided by the delay circuit.
According to a prior approach, the delay circuits are implemented as a chain of combinational elements and a multiplexor selects the signal from the output of one of the combinational elements as the delayed signal depending on the desired delay magnitude.
Such an approach may require a large number of combinational elements to provide a large span of delays and may be unsuitable for several reasons. For example, the approach may require corresponding additional circuitry (often measured as number of gates required) to implement the combinational elements, and space constraints on the die (on which the delay circuit is fabricated) may make such requirement undesirable.
Further, the large number of components may introduce jitter, which is also undesirable. An additional disadvantage of such an approach is that the delay portion introduced by each of the combinational elements may vary depending on the changes in process, voltage and temperature (PVT), and accordingly the delay provided by the delay circuit may also vary widely with PVT.
Several aspects of the present invention provide a programmable delay circuit overcoming one or more of the disadvantages noted above.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.